Scientists reveal structure of bacterial chainmail

An
international team of scientists has uncovered the structure of the protective
protein coat which surrounds many bacteria like a miniature suit of armour.

Their
research, which is published in Nature, has far
ranging consequences in helping us understand how bacteria cause disease, and
could help us develop new vaccines.

Until
now, scientists have known very little about the structure and function of this
coat, which scientists call S-layer, despite the fact that some bacteria invest
as much as a third of their total protein production in building it.

The
team of scientists, funded in the UK by the Biotechnology and Biological
Sciences Research Council, were
able to image the S-layer of a harmless soil bacterium called Geobacillus
stearothermophilus down to the scale of a single atom. They revealed that
the individual proteins of the protective layer hook together much like the
chainmail of a medieval knight.

Dr Stefan
Howorka (UCL Chemistry) led the work in the UK. He explains
“These protein coats have remained quite mysterious to scientists even though
they are found on a huge variety of bacteria.

"Using advanced imaging
techniques, we have uncovered for the first time the structure of an S-layer in
remarkable detail showing that it is put together just like chainmail. This
miniscule layer provides a flexible coat of armour for the bacteria which also
allows important nutrients and other substances in and out.”

Now that we have worked out how to obtain the structure of the S-layer in one bacterium, scientists are working to reveal the structure of the protein coats of other species.

Dr Stefan Howorka

This
chainmail coat supports the shape of bacteria and protects them from
environmental hazards. The coat is also thought to be important in allowing
many pathogenic bacteria to infect cells, helping germs to stick to and slide
into human or animal cells where they can wreak havoc. Other pathogens coat themselves with a
protein lattice that makes them invisible to the radar of the immune system.

Dr
Howorka continues “Now that we have worked out how to obtain the structure of
the S-layer in one bacterium, scientists are working to reveal the structure of
the protein coats of other species. At the top of the priority list is for us
to uncover the bacterial armour of pathogens like C. difficile and Bacillus
anthraci, the bug which
causes anthrax. Once we know how the armour of these bacteria fits
together we might be able to find a chink to target with new antibiotics and
vaccines.”

The
remarkable structure of the S-layer coat also holds promise as a carrier for
vaccines. The proteins which form the chainmail links of the S-layer arrange
themselves into the protective coat which means it is relatively easy to create
harmless vessels from S-later sheets.

Professor
Douglas Kell, BBSRC Chief Executive said “This work is a great example of how
important it is to study the secrets of how nature fits together at the most
minute scale. By revealing how things look we can gain an insight into how they
work. Understanding how nature works is going to be crucial in combating many
of the great challenges facing society, including the effort to keep people fit
and healthy into old age.”